In a new venture for the northeast, Dominion Resources Inc. (DRI) plans to construct salt caverns in Clinton and Tioga counties in rural northern Pennsylvania to hold supplies of natural gas.
Before launching this Storage Factory project DRI, headquartered in Richmond, Va., had traditionally utilized depleted storage fields whereby it re-used old rock formations that once held natural gas.
The typical underground storage field is 1 to 2 mi. (1.6 to 3.2 km) in diameter and 20,000 ft. (610 m) deep.
“These storage fields are adapted so that we can inject natural gas in the summer and withdraw it in the winter,” said Dan Donovan, manager of media relations of the company.
“Dominion manages the largest depleted field storage system in North America, located mostly in Pennsylvania, West Virginia and Ohio, where the U.S. natural gas industry began and where there are lots of depleted fields.
“Salt storage is mainly used in areas where there are no depleted fields, yet there are underground salt formations,” Donovan continued.
“These are usually in the producing areas around the Gulf of Mexico or in northern states like Michigan and New York. What we are doing with the Storage Factory project is bringing salt storage technology to an area that traditionally relied on depleted field storage.
“There are many salt deposits thereabouts with salt factories around them, mostly across the border in New York State,” he said.
Advantages of Salt Storage Facilities
Donovan described the process of constructing this type of storage facility.
“You must first find a suitable underground salt formation. Then you must create a ’salt cavern’ within the formation. This is done by using water to dissolve and extract a certain amount of salt from the deposit, leaving a large empty space in the formation, in a process known as ’salt cavern leaching,’” he said.
“For this project there will be some excavation, but the main work will be drilling and pipe laying. We will be using water from an area reservoir to leach out the salt, so piping to the reservoir will be needed,” he explained.
“Then once the caverns are finished we will lay pipes connecting them to our system. We usually contract that work out to one of several professional pipeline construction companies. For now, there are seven and a half miles of pipeline in the plan.”
In addition to the work mentioned, a compressor station to handle injection and withdrawal of gas and various structures to process and house the salt products will be built.
One difficulty facing Dominion’s project is disposal of the brine created by this process, but the company plans to dehydrate it and market the salt.
Once created, a salt cavern offers very high deliverability, since natural gas stored in salt caverns can be more readily and quickly withdrawn and the caverns replenished with natural gas quicker than other types of storage facilities. Moreover, salt caverns can readily begin the flow of gas on as little as one hour’s notice, which is useful in emergency situations or during unexpected short-term demand surges.
In addition, its contents can be stored at higher pressures than in depleted natural gas storage fields, allowing gas to be withdrawn more quickly, an important point given the type of cold weather experienced during winter.
“Construction is not scheduled to begin until 2009, so subcontractors have not yet been chosen,” Donovan said.
However, the company estimates 200 construction jobs will be created in the first two years of the project and it is anticipated 75 to 100 full-time employees will be needed to run the storage facility.
Dominion employees will supervise and coordinate the work, the cost of which will be between $500 million and $700 million, depending on how many caverns are built.
The company intends to start with two, beginning the work two years from now with a completion date of 2011, and building more caverns as the market demands them. Depending how many are needed, the project could last until 2028, with the first two caverns expected to be in service in 2014.
The first phase of the Storage Factory job will add 11.2 billion cu. ft. of gas to Dominion’s storage capacity, with the project eventually increasing it by up to 50 billion cu. ft. CEG